Expandable introducer sheath for medical device

ABSTRACT

An expandable medical sheath can include a sheath body having a lumen that extends between proximal and distal ends of the sheath. The sheath can have first and second members where the first member has a different elastic modulus than the second member such that one provides elasticity to the sheath and the other provides column strength. The first and second members can be coupled together in alternating sections to form the tubular sheath or the stiffer members can be embedded in the elastic member along all or a portion of the longitudinal length of the sheath. The sheath can automatically move to an expanded state to allow a larger diameter medical device to pass through the lumen, and once through the sheath can automatically return to its initial diameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/917,042, filed Mar. 9, 2018, which application claims priority toU.S. provisional application No. 62/470,026, filed Mar. 10, 2017, thecontent of each of which is hereby incorporated by reference herein inits entirety.

BACKGROUND OF THE INVENTION

A medical device, such as an intracardiac heart pump assembly, can beintroduced into a patient in various ways. In general, a heart pump canbe introduced in the heart to pump blood from the heart into a vessel tosupport the function of the heart. When deployed in the heart, a heartpump assembly pulls blood from the left ventricle of the heart andexpels blood into the aorta, or pulls blood from the inferior vena cava(IVC), bypasses the right atrium and right ventricle, and expels bloodinto the pulmonary artery. Heart pump assemblies are introducedsurgically or percutaneously during a cardiac procedure through thevascular system. In one common approach, pump assemblies are inserted bya catheterization procedure through the femoral artery using a sheath,such as a peel-away introducer sheath. The sheath can alternatively beinserted in other locations such as in the femoral vein or any path fordelivery of a pump for supporting either the left or right side of theheart.

The peel-away introducer sheath can be inserted into the femoral arterythrough an arteriotomy to create an insertion path for the pumpassembly. A portion of the pump assembly is then advanced through aninner lumen of the introducer and into the artery. Once the pumpassembly has been inserted, the peel-away introducer sheath is peeledaway. A repositioning sheath can then be advanced over the pump assemblyand into the arteriotomy. Replacing the introducer sheath and therepositioning sheath during insertion of a medical device can preventblood clot formation which would otherwise occur in the introducersheath, and prevent or reduce bleeding at the insertion site in the skinand/or at the insertion site within the vessel because of betterfixation of the sheath to the patient when used with a hemostatic valve.

Since peel-away introducer sheaths are not radially expandable, theinner diameter of the peel-away introducer sheath must always be largeenough to accommodate the passage of the largest diameter portion of thepump assembly such as the pump head even if other parts of the pumpassembly, such as the catheter, have a significantly smaller diameter.This means that once the pump is inserted, the peel-away introducercreates an opening that has an outer diameter that is wider thannecessary to allow passage of the pump catheter into the vessel.Accordingly, the peel-away introducer sheath is peeled away and replacedwith a lower-profile repositioning sheath. But peeling away theintroducer has several disadvantages. For example, peel-away introducerscan peel too easily and risk being torn prematurely, leading to bleedingor vascular complications. On the other hand, peel-away introducers mayrequire excessive force to peel away. If a physician applies too muchforce, when the introducer finally gives, the physician mayinadvertently shift the position of the pump within the heart. Having topeel away the introducer also complicates the design of the hemostaticvalve located in the hub of the introducer which also needs to separate.Additionally, the peel away action is an added step that the user mustbe aware of and trained on, and which requires added time to perform.Further, the need for a repositioning sheath to guide and/or repositionthe pump within the heart adds complexities to the intravascularprocedure due to the above-described multi-step nature of insertion of arepositioning sheath.

Further, if a peel-away introducer sheath is required, there is also alarger arteriotomy opening to close after the system is removed. Thelarger size of the peel away sheath can be intimidating to some usersand carries a negative perception that may limit adoption. To have aclose fit to the delivery catheter body and to minimize thecross-section of the repositioning sheath through most of the indwellinglength during longer term dwell, the inner diameter of the repositioningsheath is smaller than the peel away sheath. This prevents removal ofthe pump without also removing the repositioning sheath which losesaccess to the vessel and requiring the immediate attention to closingthe access site upon system/sheath removal.

Some medical introducers for applications other than inserting heartpumps have expandable sheath bodies which may expand radially to allowpassage of percutaneous devices into the patient's vasculature. Theseintroducers are inserted having inner diameters smaller than the outerdiameter of the device being introduced. The introducers expand to allowpassage of the device through the sheath and into the vasculature andthen shrink again after the device has passed. In the current state,these expandable introducers are for relatively short term use and arestand-alone components. Since the current expandable sheaths areintended for short term use, they are not configured for preventingthrombosis between the sheath body and an indwelling catheter.Additionally, some current expandable sheaths are completely flexibleand therefore do not provide any rigidity within their structure therebyrequiring the use of a repositioning sheath during insertion of apercutaneous medical device. Furthermore, the current expandable sheathsdo not include means for sealing the arteriotomy for long durations orfor preventing migration of the inserted device (in and out of thevessel).

SUMMARY OF INVENTION

Systems, devices and methods for insertion of a medical device (e.g.,intravascular medical device) are presented. The devices are deliveredthrough an expandable introducer sheath. Use of an introducer sheathcapable of expansion allows a smaller puncture size to be used forinsertion and can allow the vessel to more easily recoil to a smallerdiameter after insertion of the pump. Additionally, because the medicaldevice only momentarily passes through the vessel wall, the opening inthe vessel is expected to be smaller than if a larger non-expandablesheath is used. Still further, since the medical device only momentarilypasses through the vessel, if friction between the device, sheath, andvessel wall is minimized, there is a reduced axial load and reducedstress on the vessel. That is, the sheath is a smaller size and is notpushing or pulling the vessel along the axis of the insertion/removalpath and instead, when the device passes through the vessel, the vesselis expanded outward radially. The expandable introducer sheath isconfigured to remain in an insertion path (e.g., an arteriotomy) forrelatively long durations (e.g., >1 hr, >2 hr, >6 hr, or any suitableduration).

Since the expandable introducer sheath need not be removed, the risk ofpremature peel-away is essentially eliminated and the risk of shiftingthe introduced device inadvertently (e.g., by overuse of force duringpeel-away) is reduced or eliminated. Furthermore, allowing theexpandable introducer sheath to remain in an insertion path simplifiesthe use of the introduced device by reducing the number of steps in theinsertion procedure, namely by eliminating the peel-away process.

In a first aspect, an expandable medical sheath includes a sheath bodyhaving an inner surface and an outer surface, the inner surface defininga lumen that extends between proximal and distal ends of the sheath. Themedical sheath also includes first and second members, each disposedbetween the inner and outer surfaces of the sheath and each extendingbetween the proximal and distal ends of the sheath, the first membercomprising a first material and the second member comprising a secondmaterial. The sheath is expandable from an unexpanded state to anexpanded state to allow the passage of a portion of a medical devicethrough the lumen, the portion of the medical device having a transversecross-sectional area larger than a transverse cross-sectional area ofthe lumen when the sheath is the unexpanded state.

The non-homogeneous structure of the sheath body allows for the sheathto expand to the expanded state during the passage of the medical devicein the lumen of the sheath body, and return to the unexpanded state oncethe medical device leaves the lumen of the sheath body. This momentaryexpansion of the sheath body minimizes the size of the arteriotomyrequired when inserting the sheath into the vasculature of the patient.This also minimizes damage to a vessel wall as a smaller opening wouldbe required to accommodate the sheath body in the unexpanded state,thereby minimizing thrombotic occlusion of the vessel. A smaller openingalso minimizes the time to reach hemostasis after removal of the medicaldevice.

Such an expandable sheath also does away with the need for theconventional set up of having multiple sheaths, such as a peel-awayintroducer sheath and a repositioning sheath for the introduction of amedical device (e.g. a percutaneous heart pump) into the arteriotomy.Such an expandable sheath also allows a repositioning sheath to be usedin conjunction with it, if necessary. Once the expandable sheath ispositioned in an arteriotomy, it maintains access to a vessel even afterthe medical device is removed, should such access be required for othermedical procedures. This increases procedural efficiency of any medicalprocedure as there is no need to peel away the introducer sheath for theinsertion of a repositioning sheath each time access to the arteriotomyis required. Furthermore, more accurate repositioning of the medicaldevice can be achieved with the expandable introducer sheath as theexpandable introducer sheath is fixed in position once inserted whereasthe insertion of a separate repositioning sheath does involve multiplesteps where chances of misplacing the medical device are significantlyhigher.

The expandable sheath therefore removes the need for an introducersheath and a repositioning sheath during any medical procedure requiringaccess to an arteriotomy of a patient. Infection can thus be minimizedas an introducer sheath (after being peeled away) will not be restingoutside the patient after insertion of a repositioning sheath during amedical procedure. The effective consolidation of the introducer sheathand the repositioning sheath into a single device can decrease the costsinvolved during a medical procedure. Further, since only a single sheathis required to gain arteriotomic access to a vessel, less bleeding maybe involved during long term use of a percutaneous medical device suchas a heart pump.

According to a first implementation of the present disclosure, there isprovided an expandable medical sheath comprising a sheath body having aninner surface and an outer surface, the inner surface defining a lumenthat extends between proximal and distal ends of the sheath. Theexpandable sheath also comprises first and second members, each disposedbetween the inner and outer surfaces of the sheath and each extendingbetween the proximal and distal ends of the sheath, the first membercomprising a first material and the second member comprising a secondmaterial. Here the sheath is expandable from an unexpanded state to anexpanded state to allow the passage of a portion of a medical devicethrough the lumen, the portion of the medical device having a transversecross-sectional area larger than a transverse cross-sectional area ofthe lumen when the sheath is in the unexpanded state.

In some implementations, the first material has a higher elastic modulusthan the second material. In other implementations, the first materialcomprises at least one of: polyether ether ketone (PEEK), a polyetherblock amide (such as PEBAX), a polyethylene material, a high-densitypolyethylene (HDPE) material, a medium-density polyethylene (HDPE)material, a low-density polyethylene (LDPE) material, a crack-resistantmaterial, a material with a low coefficient of friction, and a materialwith an elastic modulus of about 40 ksi. In certain implementations thesecond material comprises at least one of: ethylene-vinyl acetate (EVA),styrene-butadiene copolymer (SBC), synthetic rubber, an elastomer, anelastic material, a material with an elastic modulus of about 1.6 ksi,and a material with a yield strain in excess of 200%. In otherimplementations, the sheath automatically returns to the unexpandedstate after passage of the portion of the medical device.

In certain implementations, the expandable sheath also comprises aplurality of first members and a plurality of second members, theplurality of first members being equal to in number to the plurality ofsecond members. In some implementations, the first and second membersare arranged symmetrically in alternating sections about a longitudinalaxis of the sheath. In other implementations, the first and secondmembers are arranged non-symmetrically in alternating sections about alongitudinal axis of the sheath. In some implementations, the secondmaterial encapsulates alternating sections of the first material.According to certain implementations, a diameter of the outer surface atthe proximal end of the sheath is larger than a diameter of the outersurface at the distal end of the sheath, when the sheath is in theunexpanded state. In some implementations, the sheath is radiallyexpandable, while the length of the sheath remains substantiallyunchanged when the sheath expands.

In some implementations, the expandable sheath comprises a hub coupledto the proximal end of the sheath, the hub having at least onehemostatic valve in communication with the lumen of the sheath. In otherimplementations, the inner surface has an irregular geometry to minimizecontact between the sheath body and the medical device. In certainimplementations, the inner surface comprises at least one rib extendingbetween proximal and distal ends of the sheath. In otherimplementations, the expandable sheath comprises a tip attached to thedistal end of the expandable sheath. In some implementations, the tipcomprises at least one of: ethylene-vinyl acetate (EVA),styrene-butadiene copolymer (SBC), synthetic rubber, an elastomer, anelastic material, a material with an elastic modulus of about 1.6 ksi,and a material with a yield strain in excess of 200%.

In certain implementations, the tip comprises an inner surface defininga tip lumen that extends between proximal and distal ends of the tip,the tip lumen being in fluid communication with the lumen of theexpandable sheath. In other implementations, an outer diameter of theproximal end of the tip is larger than an outer diameter of the distalend of the tip such that the tip is tapered. In further implementations,a diameter of the inner surface at the proximal end of the tip is largerthan a diameter of the inner surface at the distal end of the tip. Incertain implementations, the tip comprises the second material. In otherimplementations, the first material is substantially stiffer than thesecond material, and the second material is substantially more elasticthan the first material. In certain implementations, the length of thesheath remains substantially unchanged when the sheath expands from theunexpanded state to the expanded state.

According to a further implementation of the present disclosure, thereis provided an expandable medical sheath comprising a sheath body havingan inner surface and an outer surface, the inner surface defining alumen that extends between proximal and distal ends of the sheath. Theexpandable sheath further comprises a plurality of first members and aplurality of second members, each disposed between the inner and outersurfaces of the sheath, each first member comprising a first materialand each second member comprising a second material, and each of thefirst and second members being alternately arranged around the lumen.Here the sheath is expandable from an unexpanded state to an expandedstate to allow the passage of a portion of a medical device through thelumen, the portion of the medical device having a transversecross-sectional area larger than a transverse cross-sectional area ofthe lumen when the sheath is in the unexpanded state.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 shows an isometric view of an illustrative prior art medicaldevice;

FIG. 2 shows an isometric view of an illustrative expandable sheath;

FIG. 3A shows a transverse cross section of the illustrative expandablesheath of FIG. 2 in an unexpanded state;

FIG. 3B shows a transverse cross section of the illustrative expandablesheath of FIG. 2 in an expanded state;

FIG. 4A shows a transverse cross section of the illustrative expandablesheath of FIG. 2 with a flexible member and a rigid member;

FIG. 4B shows a transverse cross section of the illustrative expandablesheath of FIG. 2 with two flexible members and two rigid membersarranged in a symmetric manner;

FIG. 4C shows a transverse cross section of the illustrative expandablesheath of FIG. 2 with two flexible members and two rigid membersarranged in a non-symmetric manner;

FIG. 5 shows a lateral cross section of an illustrative expandablesheath for arterial access for a medical device such as the device ofFIG. 2;

FIG. 6 shows a transverse cross section of the illustrative expandablesheath of FIG. 2 which indicates the anticipated strain during expansionof the sheath body;

FIG. 7 shows an isometric view of a distal end of the illustrativeexpandable sheath of FIG. 2;

FIG. 8 shows an isometric view of a proximal end of the illustrativeexpandable sheath of FIG. 2;

FIG. 9 shows an isometric view of a proximal end of the illustrativeexpandable sheath of FIG. 2 coupled to a flexible portion of a hubassembly;

FIG. 10A shows a lateral cross section of an illustrative hub assemblycoupled to the proximal end of the illustrative expandable sheath ofFIG. 2;

FIG. 10B shows an isometric view of the illustrative hub assembly ofFIG. 10A;

FIG. 11 shows an isometric view of a distal end of the illustrativeexpandable sheath of FIG. 2 assembled with a dilator during insertion ofthe expandable sheath;

FIG. 12 shows an isometric view of a distal end of a dilator used duringinsertion of the expandable sheath of FIG. 2;

FIG. 13 shows a cross sectional view of the illustrative expandablesheath of FIG. 2 with the hub assembly of FIGS. 9, 10A and 10B coupledto a hub of a medical device inserted into the expandable sheath;

FIGS. 14A to 14C show transverse cross sections of further aspects ofthe expandable sheath according to the present disclosure; and

FIG. 15 shows an illustrative method for inserting a medical device intoan arteriotomy using the expandable sheath of FIG. 2.

DETAILED DESCRIPTION

To provide an overall understanding of the systems, method, and devicesdescribed herein, certain illustrative embodiments will be described.Although the embodiments and features described herein are specificallydescribed for use in connection with a percutaneous heart pump system,it will be understood that all the components and other featuresoutlined below may be combined with one another in any suitable mannerand may be adapted and applied to other types of medical devices such asTAVR delivery systems, cardiac therapy and cardiac assist devices,including balloon pumps, cardiac assist devices implanted using asurgical incision, and the like.

The systems, methods and devices described herein provide an expandablesheath assembly for the insertion of a medical device (e.g., apercutaneous heart pump) into a blood vessel through a vessel aperture.The expandable medical sheath comprises a sheath body having an innersurface and an outer surface, the inner surface defining a lumen thatextends between proximal and distal ends of the sheath. The medicalsheath also includes first and second members, each disposed between theinner and outer surfaces of the sheath and each extending between theproximal and distal ends of the sheath, the first member comprising afirst material and the second member comprising a second material. Thesheath is expandable from an unexpanded state to an expanded state toallow the passage of a portion of a medical device through the lumen,the portion of the medical device having a transverse cross-sectionalarea larger than a transverse cross-sectional area of the lumen when thesheath is the unexpanded state.

The non-homogeneous structure of the sheath body allows for the sheathto expand to the expanded state during the passage of the medical devicein the lumen of the sheath body, and return to the unexpanded state oncethe medical device leaves the lumen of the sheath body. This momentaryexpansion of the sheath body minimizes the size of the arteriotomyrequired when inserting the sheath into the vasculature of the patient.This also minimizes damage to a vessel wall as a smaller opening wouldbe required to accommodate the sheath body in the unexpanded state,thereby minimizing thrombotic occlusion of the vessel. A smaller openingalso minimizes the time to reach hemostasis after removal of the medicaldevice. Such an expandable sheath does away with the need for theconventional set up of having multiple sheaths, such as a peel-awayintroducer sheath and a repositioning sheath for the introduction of amedical device (e.g. a percutaneous heart pump) into the arteriotomy.Such an expandable sheath also allows such a conventional set up to beused in conjunction with it, if necessary. Once the expandable sheath ispositioned in an arteriotomy, it maintains access to a vessel even afterthe medical device is removed, should such access be required for othermedical procedures. This increases procedural efficiency of any medicalprocedure as there is no need to re-gain alternative access or re-inserta second introducer in the same access site.

In certain embodiments, the expandable sheath is compressed to acompressed state during insertion into the vasculature of the patient.Once inserted, the expandable sheath expands to a resting configuration.The resting configuration of the sheath body allows for the sheath toexpand to an expanded state during the passage of the medical device inthe lumen of the sheath body, and return to the resting configurationonce the medical device leaves the lumen of the sheath body. Thecompressed state of the sheath body also minimizes the size of thearteriotomy required when inserting the sheath into the vasculature ofthe patient. This also minimizes damage to a vessel wall as a smalleropening would be required to accommodate the sheath body in theunexpanded state, thereby minimizing thrombotic occlusion of the vessel.A smaller opening also minimizes the time to reach hemostasis afterremoval of the medical device.

The expandable sheath therefore removes the need for an introducersheath and a repositioning sheath during any medical procedure requiringaccess to an arteriotomy of a patient. Infection will thus be minimizedas a repositioning sheath will not be resting outside the patient priorto the removal of the peel away sheath during a medical procedure. Theeffective consolidation of the introducer sheath and the repositioningsheath into a single device undoubtedly decreases the costs involvedduring a medical procedure. Further, since only a since sheath isrequired to gain arteriotomic access to a vessel, less bleeding would beinvolved during long term use of a percutaneous medical device such as aheart pump.

FIG. 1 shows an illustrative mechanical assist device (MAD) such as apercutaneous pump 100 according to certain implementations. The pump 100comprises a pump handle 110, a pump head 130, a catheter 120 connectingthe pump handle 110 to the pump head 130, and a connecting hub 160. Thecatheter 120 is tubular and has a substantially uniform outer diameter.The catheter 120 enables the pump head 130 and the pump handle 110 to bein electro-mechanical communication. The pump handle 110 is incommunication with control circuitry which allows the control of thepump head 130. The pump head 130 contains electro-mechanical componentsthat enable the device to perform various tasks within the body of apatient, such as pump blood from a location within the body. The pumphead 130 has a diameter 140 that is larger than the diameter 150 of thecatheter 120. An example of such a percutaneous pump is the Impella 2.5™system (Abiomed, Inc., Danvers, Mass.). It will be understood that whilea percutaneous heart pump is described herein, any other percutaneousmedical device can be used in conjunction with the present disclosure.

FIG. 2 shows an illustrative expandable sheath 200 according to certainimplementations. The expandable sheath 200 comprises a sheath body 210having a distal end 220 and a proximal end 230. A flexible tip 240having an internal lumen is attached to the distal end 220 of the sheathbody 210. A hub assembly 250 is coupled to the proximal end 230 of thesheath body 210. The hub assembly 250 comprises a flexible portion 260and a rigid portion 270. The flexible portion 260 couples the proximalend 230 of the sheath body 210 to the distal end of the rigid portion270 of the hub assembly 250. The sheath body 210 has a longitudinal axis290. In certain implementations, the sheath body 210 is tubular.

FIG. 3A shows a transverse cross-section of the sheath body 210. Thesheath body 210 has an inner surface 204 and an outer surface 206. Theinner surface 204 defines a lumen 202 that extends between the proximalend 230 and the distal end 220 of the sheath body 210 for the momentarypassage of a portion of a medical device, such as the percutaneous pump100 of FIG. 1. The lumen 202 of the sheath body 210 has an internaldiameter 218. The sheath body 210 has an outer diameter 219. The sheathbody 210 is non-homogenous. The sheath body 210 comprises flexiblesections 211-217 and rigid sections 281-287. The flexible sections211-217 provide a means of expansion of the internal diameter 218 of thesheath body 210 and return to its unexpanded state thereby allowing thepassage of a medical device having a larger diameter than the innerdiameter 218 of the sheath 200. The rigid sections 281-287 aresubstantially stiffer than the flexible sections 211-217. The rigidsections 281-287 provide column strength and stiffness for axialcompressive loading. Such axial loading occurs during insertion of amedical device 100 into the expandable sheath 200. The rigid sections281-287 therefore resist buckling during axial insertion of the medicaldevice 100 into the sheath 200. The flexible sections 211-217 and therigid sections 281-287 are present in equal number. Each of the flexible211-217 and rigid 281-287 sections extend along the length of the sheathfrom the proximal end 230 to the distal end 220. Additionally, each ofthe flexible 211-217 and rigid 281-287 sections are disposed between theinner surface 204 and the outer surface 206 of the sheath body 210. Theflexible sections 211-217 and the rigid sections 281-287 are alternatelyarranged to form the sheath body 210 such that each flexible section211-217 is adjacent to a rigid section 281-287, and, similarly, eachrigid section 281-287 is adjacent to a flexible section 211-217.Alternative configurations of the expandable sheath will be detailed inthe sections that follow and with reference to FIGS. 14A to 14C.Further, while a single lumen 202 has been described, it will beunderstood that multiple lumens may be present in the sheath body 210.Such multiple lumens are described in U.S. patent application Ser. No.14/827,741, entitled “Dual Lumen Sheath for Arterial Access,” the entirecontents of which are hereby incorporated by reference. Multiple lumensfacilitate the use of a stylet and/or a guide wire with the expandablesheath 200.

The flexible sections 211-217 comprise a flexible material. The flexiblematerial is an elastic material with an elastic modulus of about 1.6ksi. Ksi is a unit of pressure, representing thousands of pounds persquare inch. In some implementations, the flexible material is amaterial with a yield strain of about 200%. In some implementations, theflexible material contains a radiopaque filler such as bismuthoxychloride or barium sulfate in concentrations of 5% to 40% by weight.In certain implementations, the flexible material comprises any one of:ethylene-vinyl acetate (EVA), styrene-butadiene copolymer (SBC),synthetic rubber, or any other elastomer. The rigid sections 281-287comprise a rigid material. The rigid material is a polyethylene orpolyurethane material with an elastic modulus of about 40 ksi. In someimplementations the rigid material contains a radiopaque filler such asbismuth oxychloride or barium sulfate in concentrations of 5% to 40% byweight. In some implementations, the rigid material is any one of ahigh-density polyethylene (HDPE) material, a medium-density polyethylene(MDPE) material, a low-density polyethylene (LDPE) material, polyetherether ketone (PEEK), and a polyether block amide (such as PEBAX). Incertain implementations, the rigid material is a crack-resistantmaterial. In some implementations, the rigid material may also be amaterial with a low coefficient of friction.

In some implementations, the inner surface 204 of the sheath body 210may have an irregular geometry to minimize contact with a medical device(e.g., medical device 100) that is advancing through the lumen 202. Suchirregular geometry may include structures that span at least a portionof the longitudinal length of the sheath body 210. Such structures mayinclude ribs, projections, indentations, for example, that reduce theamount of contact the inner surface 204 of the sheath body 210 makeswith a medical device 100 that is advanced through the lumen 202. In oneimplementation, the inner surface 204 of the sheath body 210 may beprovided with at least one rib or projection that runs along at least aportion of the longitudinal length of the sheath 210. Such structuresmay appear as raised features that protrude from the inner surface 204of the sheath body 210. In other implementations, the inner surface 204of the sheath body 210 may be provided with at least one indentationthat runs along at least a portion of the longitudinal length of thesheath 210. Such structures may appear as recessed features that appearas depressions on the inner surface 204 of the sheath body 210. Infurther implementations, a combination of projections and indentationsmay be provided along at least a portion of the longitudinal length ofthe sheath body 210.

The arrangement of the flexible 211-217 and rigid 281-287 sections ofthe sheath body 210 enable the sheath 200 to radially expand about thelongitudinal axis 290 when a portion of a medical device 100 that islarger than the transverse cross-sectional area of the lumen 202 when inan unexpanded state is introduced into the sheath body 210. Such radialexpansion occurs when the largest diameter 140 of the medical device 100is greater than the unexpanded diameter 218 of the lumen 202. It canalso be said that such radial expansion occurs when the transversecross-sectional area of the portion of the medical device 100 is largerthan the transverse cross-sectional area of the lumen 202 when in anunexpanded state. Thus when the medical device 100 is inserted into thelumen 202 of the sheath 200, the lumen 202 expands and the diameter ofthe lumen 202 increases from 218 to 218′ as shown in FIG. 3B. Theexternal diameter 219 of the sheath body 210 increases from 219 to 219′.In this expanded state, the flexible sections 211-217 are forced todeform so as to accommodate the medical device 100 in the lumen 202.Such deformation is indicated by the radially outward arrows B in FIG.3B. When the flexible sections 211-217 deform, they increase in width(see difference between section 211 and expanded section 211′, forexample), thereby causing the overall diameter 218 of the lumen 202 toincrease to 218′ as depicted in FIG. 3B. It naturally follows that whenthe diameter 218 of the lumen 202 increases to 218′, the transversecross-sectional area of the lumen 202 also increases. The increasedtransverse cross-sectional area of the lumen 202 enables the portion ofmedical device 100 that is larger than the transverse cross-sectionalarea of the lumen 202 when in an unexpanded state to move within thesheath body 210. FIG. 3B illustrates the deformation of the flexiblesections 211-217 in FIG. 3A to sections 211′-217′ in FIG. 3B. Suchdeformation of the flexible sections 211-217 is within elastic limit ofthe flexible material used for the flexible sections 211-217. Theseflexible sections 211-217 therefore do not permanently deform. Thus,after the portion of the medical device 100 that is larger than thetransverse cross-sectional area of the lumen 202 when in an unexpandedstate has passed through the sheath body 210, the deformed flexibleportions 211′-217′ automatically return to their unexpanded width asshown in FIG. 3A, and the expanded diameter 218′ of the lumen 202decreases to 218 as indicated in FIG. 3A. It will be understood that thesheath body 210 will return from the expanded state to the unexpandedstate passively and with no intervention by using elastic straindeveloped in the flexible sections 211-217. It should also be noted thatdue to the alternate arrangement of the rigid sections 281-287 and theflexible sections 211-217, and their respective material compositions(i.e. that the rigid sections 281-287 comprise a material that issubstantially stiffer than the material used for the flexible sections211-217), the length of the sheath body 210 remains substantiallyunchanged when the sheath expands from the unexpanded state (withdiameter 218) to the expanded state (with diameter 218′).

In FIG. 3A, seven flexible sections 211-217 and seven rigid sections281-287 are shown. However it will be understood that any number offlexible 211-217 and rigid 281-287 sections can be used in connectionwith the present disclosure. Additionally, these sections can bearranged in a symmetrical or non-symmetrical manner about thelongitudinal axis 290 of the sheath body 210. For example, in certainimplementations as shown in FIG. 4A, the sheath body 420 comprises oneflexible section 422 and one rigid section 424. FIG. 4B illustratesanother implementation in which the sheath body 440 comprises twoflexible sections 442, 443 and two rigid sections 444, 445. In FIG. 4B,the flexible and rigid sections 442-445 are arranged in a symmetricmanner about the longitudinal axis of the sheath body 440 (not shown).FIG. 4C illustrates an alternative non-symmetrical arrangement offlexible sections 462, 463 and rigid sections 464, 465 of the sheathbody 460.

FIG. 5 shows a lateral cross-sectional view of the sheath body 210 takenalong the line A-A′ as shown in FIGS. 3A and 3B. The figure showsflexible section 211 and rigid section 284 when the sheath body 210 isunexpanded (as shown in FIG. 3A). In the unexpanded state, the lumen 202has an unexpanded diameter 218. When a portion of a medical device 100is inserted into the sheath body 210, the flexible sections 211-217deform thereby increasing the diameter of lumen 202 to 218′. Inparticular, flexible section 211 deforms to 211′ while the rigid sectiondoes not substantially deform (as shown in FIG. 3B). The flexible tip240 and the flexible portion 260 of the hub assembly 250 are also shownin FIG. 5, and will be discussed in the sections that follow.

FIG. 6 illustrates the anticipated strain along a transversecross-sectional area of the sheath body 210 when the sheath body 210 isin the expanded state for the passage of the medical device 100 in thelumen 202 (as depicted in FIG. 3B). Rigid sections 281-287 show littleto no strain (indicated by the darker shading), while deformed flexiblesections 211′-217′ show high levels of strain (indicated by the lightershading).

FIG. 7 shows a perspective view of the sheath body 210 which terminateswith a flexible tip 240. The tip 240 comprises a proximal end 242, adistal end 244, an outer surface 248 and an inner surface 249. The innersurface 249 defines an opening 241 with an inner diameter 243, and theouter surface 248 has an outer diameter 245. The proximal end 242 of thetip 240 is coupled to the distal end 220 of the sheath body 210 suchthat the lumen 202 and the opening 241 of the tip 240 are seamlessly incommunication with each other. This allows for easy passage of themedical device 100 as it leaves the sheath 200 and progresses into thevasculature of a patient. The inner surface 249 of the tip 240 isslightly tapered such that the inner diameter 243 is larger at theproximal end 242 than at the distal end 244 of the tip 240. This createsa slight inference fit with the smallest diameter on the medical device100. This slight inference of the distal tip 240 with the medical device100 helps seal any fluid or blood from entering the opening 241 andhence the lumen 202 while allowing the lumen 202 to be flushed withfluid. The outer surface 248 of the tip 240 is also tapered towards thedistal end 244 such that the outer diameter 245 is larger at theproximal end 242 than at the distal end 244. The distal end 244 of thetip 240 terminates at a leading edge 246. The outer diameter of theleading edge 246 has a radius to facilitate smooth insertion of thesheath 200 into the vasculature of a patient. The tip 240 is highlyresilient and will not exhibit permanent deformation (such as flaring orsplitting). In certain implementations, the tip 240 comprises the sameflexible material as the flexible sections 211-217 of the sheath body210. Further, the tapered surfaces 248, 249 result in thinning of thewalls of the tip 240 towards the distal end 244. This allows for lesstraumatic retrieval of an oversized medical device during removal fromthe vasculature of a patient. In certain implementations, the tip 240comprises a flexible material. The flexible material is an elasticmaterial with an elastic modulus of about 1.6 ksi. In someimplementations, the flexible material is a material with a yield strainof about 200%. In certain implementations, the flexible materialcomprises ethylene-vinyl acetate (EVA). In further implementations, theflexible material comprises an elastomer. In other implementations, theflexible material may comprise a material similar to that used for theflexible sections 211-217 of the sheath body 210.

FIG. 8 illustrates the proximal end 230 of the sheath body 210 accordingto certain implementations. The proximal end 230 is flared and has anouter diameter 291 that is larger than the outer diameter 219 of thesheath body 210. The flared proximal end 230 of the sheath body 210 iscoupled to the flexible portion 260 of the hub assembly 250 as shown inFIG. 9. The flared proximal end 230 enables the sheath body 210 to becoupled to the hub assembly 250. In other implementations, the flaredproximal end 230 of the sheath body 210 is coupled to the rigid portion270 of the hub assembly 250, with the flexible portion 260 residingaround the sheath.

FIGS. 9, 10A and 10B show the hub assembly 250 coupled to the proximalend 230 of the sheath body 210. The hub assembly 250 comprises aflexible portion 260 and a rigid portion 270. The hub assembly 250 hasan internal conduit 252 that is in fluid communication with the lumen202 when the hub assembly 250 is coupled to the sheath body 210. Theinternal conduit 252 of the hub assembly 250 comprises a lumen 263formed within the flexible portion 260 and a lumen 273 formed within therigid portion 270. The lumens 263, 273 are in fluid communication witheach other. The flexible portion 260 comprises an opening 261, aproximal face 262, a distal face 264, a bottom surface 265, and wings266, 267. Each of the wings 266, 267 has at least one securing hole 268,269. The bottom surface 265 is attached to a patient via the securingholes 268, 269 in wings 266, 267. The securing holes 268, 269 may beused to fasten the hub assembly 250 to a patient using sutures. Theflexible portion 260 is also designed to be easily attached to avascular graft with umbilical tape or sutures. This is beneficial duringaxillary insertions or any other insertions which require pump placementthrough a vascular graft. In certain implementations, otherstabilizations devices, such as surgical tape, a STATLOCK® stabilizationdevice (Bard Access Systems, Inc., Salt Lake City, Utah), or any othersuitable adhesive stabilization device may be coupled to the rigidportion 270. The bottom surface 265 is arranged to be angled relative tothe sheath body 210. In this configuration, the bottom surface 265 ofthe flexible portion 260 is at an angle 294 with the longitudinal axis290 of the sheath body 210. This helps prevent kinking of the sheathbody 210 as it orients the axis 290 of the sheath body 210 along adirection of an insertion pathway when the hub assembly 250 is fixatedto the patient. While the hub assembly 250 is described as comprising aflexible portion 260 and a rigid portion 270, it will be understood thatthe hub assembly may comprise a single unit, said unit entirelycomprising either a flexible material or a rigid material. In certainimplementations, the rigid portion 270 of the hub assembly 250 may beconfigured with a valve 296 as shown in FIG. 10A, such as a hemostaticvalve as described in U.S. patent application Ser. No. 15/245,982entitled “Hemostatic Valve for Medical Device Introducer,” the entirecontents of which are hereby incorporated by reference

The opening 261 of the flexible portion 260 of the hub assembly 250 iscoupled to or engages the flared proximal end 230 of the sheath body210. Such coupling or engagement may be achieved using any kind ofengaging mechanism such as a threaded connection, a press fit connectionor a clip-lock connection, for example. As exemplified in FIGS. 9, 10Aand 10B, the proximal face 262 of the flexible portion 260 has anexternal fit with the flared proximal end 230 of the sheath body 210,i.e. the flared proximal end 230 of the sheath body 210 fits within theopening 261 of the flexible portion 260. In this arrangement, theflexible portion 260 of the hub assembly 250 will constrain the proximalend 230 of the sheath body 210 and prevent it from expanding. Oncecoupled, the sheath body 210 will be in fluid communication with theconduit 252 of the hub assembly 250. In certain implementations, thesheath body 210 may extend through the lumen 263 in the flexible portion260 and couple to an opening in the rigid portion 270 of the hubassembly 250. In certain implementations, the flexible portion 260comprises a flexible material. In some implementations, the flexiblematerial is an elastic material with an elastic modulus of about 1.6ksi. In other implementations, the flexible material is a material witha yield strain of about 200%. In further implementations, the flexiblematerial comprises any one of: ethylene-vinyl acetate (EVA),styrene-butadiene copolymer (SBC) and synthetic rubber. In someimplementations, the flexible material comprises an elastomer, such asstyrene ethylene butylene styrene (SEBS). The rigid portion 270comprises a rigid material. In some implementations the rigid materialis a polyethylene, polyurethane or polycarbonate material with anelastic modulus of about 40 ksi. In some implementations, the rigidmaterial is any one of a high-density polyethylene (HDPE) material, amedium-density polyethylene (MDPE) material, a low-density polyethylene(LDPE) material, polyether ether ketone (PEEK), and a polyether blockamide (such as PEBAX). In certain implementations, the rigid material isa crack-resistant material. In some implementations, the rigid materialmay also be a material with a low coefficient of friction.

In certain implementations, the rigid portion 270 of the hub assembly250 has a port 292 that is in fluid communication with the internalconduit 252 of the hub assembly 250. When the sheath body 210 is coupledto the hub assembly 250, the port 282 will therefore also be in fluidcommunication with the lumen 202 of the sheath body 210. In certainimplementations, the port 282 may have a valve 293.

In certain implementations, the port 292 may be used as a flushing portwhich enables the conduit 252 and the lumen 202 to be flushed with afluid. When a portion of a medical device is inserted into theexpandable sheath 200, hemostasis may develop within the lumen 202 andthe conduit 252 in any space between the medical device and the sheath200. This may result in unwanted clotting if the medical device iscontained in the sheath for long periods of time. The port 292 thereforeenables the space to be flushed with a fluid. A pressure bag may beconnected to the port 292 using any kind of engaging mechanism (e.g.threads, clip lock, etc.). The pressure bag can be used to flush thespace between the medical device and the sheath 200 with a fluid tomaintain the patency said space thereby preventing any blood clots fromforming. Such flushing may be instantaneous or continuous. An infusionpump may be used in combination with the pressure bag to regulate theflow rate of liquid into the patient. For example, the flow rate may belimited to 1 mL/hr, 2 mL/hr, 5 mL/hr, 10 mL/hr, or any other suitableflow rate. The port can also be used to obtain measurement of bloodpressure if necessary. In other implementations, the port 292 may beused as a balloon port to inflate balloon.

The expandable sheath 200 is inserted in to the vasculature of a patientusing a dilator 1100 as shown in FIG. 11 where the sheath body 210 isassembled with the dilator 1100. The dilator 1100 is inserted into thelumen 202 of the sheath body 210 via the internal conduit 252 of the hubassembly 250. The tapered inner surface 249 of the flexible tip 240creates a slight inference fit when the dilator 1100 progressed throughthe tip 240. This creates a smooth or seamless transition from the bodyof the dilator 110 to the outer surface 206 of the sheath body 210 whenthe sheath body 210 assembled with the dilator 1100 is inserted into thepatient.

FIG. 12 illustrates an isometric view of the distal end of the dilator1100. A fully flexible tip 1200, similar to tip 240, is coupled to thedistal end of the dilator 1100. The tip 1200 defines a through hole 1210for the passage of a guide wire (not shown). The through hole 1210 isconnected to a central bore (not shown) within the dilator 1100 throughwhich a guide wire can be threaded. The tip 1200 is configured such thatit has a tapered inner wall similar to the inner surface 249 of the tip240 attached the distal end 220 of the sheath body 210. This creates aslight inference fit when the guide wire is inserted into tip 1200 fromthe dilator 1100, and provides a seamless transition from the guide wireonto the dilator 1100. The flexibility of the tip 1200 prevents damageof the dilator tip during insertion, improves track-ability of thedilator over the guide wire when maneuvering through an arteriotomy withparticularly aggressive insertion angles. The flexible tip 1200 alsoprevents vessel puncture, thereby minimizing damage to vessels. Incertain implementations the tip 1200 comprises a flexible material. Theflexible material is an elastic material with an elastic modulus ofabout 1.6 ksi. In some implementations, the flexible material is amaterial with a yield strain of about 200%. In certain implementations,the flexible material comprises any one of: ethylene-vinyl acetate(EVA), styrene-butadiene copolymer (SBC), synthetic rubber, and anelastomer.

FIG. 13 shows the expandable sheath 200 used in conjunction with amedical device such as the percutaneous heart pump 100 of FIG. 1, afterthe expandable sheath 200 has been inserted into an insertion site usingthe dilator 1100, and secured onto the patient via the flexible hub 260of the hub assembly 250. Once the expandable sheath 200 is in position,the pump head 130 is inserted into the conduit 252 of the hub assembly250, and into the lumen 202 of the sheath body 210. As the diameter 140of the pump head 130 is larger than the unexpanded diameter 218 of thelumen 202, the pump head 130 causes the sheath body 210 to expand as itprogresses through the lumen 202 from the proximal end 230 to the distalend 220. This expansion is facilitated by the flexible sections 211-217and rigid sections 281-287 that make up the sheath body 210. When thesheath body 210 expands, the diameter of the lumen 202 increases from218 to 218′, as shown in FIG. 3B. After the pump head 140 has passedthrough the sheath body 210, the lumen 202 returns to its unexpandedstate as depicted in FIG. 3A. The percutaneous pump 100 has a connectinghub 160 fixedly arranged on the catheter body 120. In certainimplementations, the connecting hub 160 is used to couple the pump 100to the hub assembly 250 where hub 160 attaches to the rigid portion 270.Such coupling may be achieved using any kind of engaging mechanism suchas a threaded connection, a press fit connection or a clip-lockconnection, for example. Such coupling provides a fluid-tight sealbetween the expandable sheath 200 and the portion of the pump 100inserted into the sheath 200. The coupling between the hub 160 of thepump 100 and the rigid portion 270 of the hub assembly 200 may also behemostatic and designed with a sealing feature such as an O-ring orinterference fit to prevent blood leaking between the sheath 200 and thecatheter body 120. In certain embodiments, once the hub assembly 250 iscoupled with the connecting hub 160, fluid can be passed through theport 292 to continuously flush blood out of the space between theexpandable sheath body 210 and the pump 100.

FIGS. 14A-14C illustrate alternative configurations of the expandablesheath 200. FIG. 14A shows a transverse cross-section of the expandablesheath body 1510 according to some implementations. The sheath body 1510is provided with a plurality of rigid sections 1521-1528 that arepartially or fully encapsulated by a flexible material 1530. Thisconfiguration of the rigid and flexible sections may be favorable to aidin manufacturability and minimization of stress concentrations at theinterface between the rigid sections and flexible section.

FIG. 14B shows a transverse cross-section of the expandable sheath body1540 according to another implementation. Sheath body 1540 contains asimilar cross-section to sheath body 1510, i.e. the sheath body 1540 isprovided with a plurality of rigid sections 1551-1558 that are partiallyor fully encapsulated by a flexible material 1570, with the exceptionthat very rigid sections 1561-1568 have been included in the sheath body1540. The very rigid sections 1561-1568 comprise a material that is morerigid than the material used for the rigid sections 1551-1558. In someimplementations, the material used for the very rigid sections 1561-1568comprises steel, stainless steel, nitinol (preferred due to itssuperelasticity), or other metal alloys. The very rigid sections1561-1568 may comprise a circular cross-section (round wire) or arectangular cross-section (flat wire). The very rigid sections 1561-1568further increase the longitudinal stiffness and increases columnstrength of the sheath body 1540. Each of the very rigid sections1561-1568 may either be fully encapsulated by the respective rigidsections 1551-1558, or they may be partially encapsulated by therespective rigid sections 1551-1558, depending on the ease ofmanufacturing. Very rigid sections may also be added to the rigidsections shown in FIGS. 3A-3B and 4A-4C in a manner similar to thatillustrated in FIG. 14B.

FIG. 14C shows a transverse cross-section of the expandable sheath body1580 according to further implementations. The sheath body 1580comprises very rigid sections 1591-1598 encapsulated by flexiblematerial 1585. Here each of the rigid sections 1591-1598 may either befully encapsulated by the flexible material 1585, or they may bepartially encapsulated by the flexible material 1585, depending on theease of manufacturing.

The sheath bodies 1510, 1540 and 1580 illustrated in FIGS. 14A-14C adoptsimilar materials to those used in respect of the sheath body 210discussed in the preceding sections. Specifically, the flexible materialis an elastic material with an elastic modulus of about 1.6 ksi(thousands of pounds per square inch). In some implementations, theflexible material is a material with a yield strain of about 200%. Insome implementations, the flexible material contains a radiopaque fillersuch as bismuth oxychloride or barium sulfate in concentrations of 5% to40% by weight. In certain implementations, the flexible materialcomprises any one of: ethylene-vinyl acetate (EVA), styrene-butadienecopolymer (SBC), synthetic rubber, or any other elastomer. The rigidsections comprise a rigid material. The rigid material is a polyethyleneor polyurethane material with an elastic modulus of about 40 ksi. Insome implementations the rigid material contains a radiopaque fillersuch as bismuth oxychloride or barium sulfate in concentrations of 5% to40% by weight. In some implementations, the rigid material is any one ofa high-density polyethylene (HDPE) material, a medium-densitypolyethylene (MDPE) material, a low-density polyethylene (LDPE)material, polyether ether ketone (PEEK), and a polyether block amide(such as PEBAX). In certain implementations, the rigid material is acrack-resistant material. In some implementations, the rigid materialmay also be a material with a low coefficient of friction.

FIG. 15 shows an illustrative method 1400 of using the expandableintroducer sheath 200. The illustrative method 1400 may be performedusing the expandable introducer sheath 200 or any other suitable sheathtool. At step S1410 a dilator such as dilator 1100 is inserted into thelumen 202 of the sheath body 210 via internal conduit 252 of the hubassembly 250. Once the dilator 1100 is inserted into the sheath body210, the assembly is inserted into a blood vessel through a percutaneousinsertion path as shown in step S1420. The blood vessel may be anartery, such as the femoral artery. The insertion path passes through ablood vessel aperture (e.g., an arteriotomy). When the assembly is inthe desired position, the dilator 1100 is removed from the lumen 202 ofthe sheath body 210 leaving the sheath body 210 in the arteriotomy.

After the dilator 1100 is removed from the sheath body 210, the lumen202 remains the same diameter in its relaxed date at its smallestinternal diameter.

Once the dilator 1100 is removed, a medical device such as apercutaneous pump may be inserted into the lumen 202 of the sheath body210 via the internal conduit 252 of the hub assembly 250, as shown instep S1440. When the widest portion 130 of the medical device 100 isinserted into the lumen 202 of the sheath 200, the lumen 202 expands andthe diameter of the lumen 202 increases from 218 to 218′ so as toaccommodate the widest portion 130 of the medical device 100, as shownin FIG. 3B. The widest portion 130 of the medical device 100 is thenadvanced right through the lumen 202 until it exits the distal end 220of the expandable sheath 200. The medical device 100 is then advancedinto the artery of the patient as desired (step S1450).

Once the medical device 100 is in position within the expandable sheath200, the expandable sheath 200 is then fastened to the patient in stepS1460. This may be done via the securing holes 268, 269 in wing 266, 267of the flexible hub 260. Such fastening may be facilitated with the aidof sutures or medical adhesive tape, for example. Additionally, incertain implementations, the expandable sheath 200 may be fixed in placewithin the arteriotomy of the patient by inflating a balloon on theouter surface of the sheath body 210.

While the expandable sheath 200 has been described in relation to apercutaneous pump, it can be envisaged that the sheath can be used witha percutaneous pump integrated with a repositioning sheath as describedin U.S. Patent Application 62/394,597 entitled “Integrated ExpandableAccess for Medical Device Introducer,” the entire contents of which arehereby incorporated by reference.

In view of the foregoing, the person of ordinary skill will appreciatethat the present disclosure provides a means to fixate mechanicaldevices in place within an expandable sheath, thereby preventing themigration of the device once inserted into the heart. Medical devices ofvarying diameters may be used with a single expandable sheath.

The foregoing is merely illustrative of the principles of thedisclosure, and the systems, methods, and devices can be practiced byother than the described embodiments, which are presented for purposesof illustration and not of limitation. It is to be understood that thesystems, methods, and devices disclosed herein, while shown for use in asystem percutaneous heart pumps, may be applied to systems, methods, anddevices for other implantable heart pumps or implantable cardiac assistdevices.

Variations and modifications will occur to those of skill in the artafter reviewing the present disclosure. The various features describedor illustrated above, including any components thereof, may be combinedor integrated in other systems. Moreover, certain features may beomitted or not implemented. The various implementations described orillustrated above may be combined in any manner.

Examples of changes, substitutions, and alterations are ascertainable byone skilled in the art and could be made without departing from thescope of the information disclosed herein. All references cited hereinare incorporated by reference in their entirety and made part of thisapplication.

1. An expandable sheath comprising: a sheath body having an inner surface and an outer surface, the inner surface defining a lumen that extends along a longitudinal axis between a proximal end and a distal end of the sheath body, the sheath body being comprised of: a first member extending between the proximal end and the distal end of the sheath body and forming the outer surface of the sheath body, the first member having an inner surface comprising a plurality of cavities extending parallel to the longitudinal axis between the proximal end and the distal end of the sheath body, and the first member comprising a first material having a first elastic modulus; a plurality of second members, each second member being at least partially encapsulated within a given cavity of the plurality of cavities of the first member and extending parallel to the longitudinal axis between the proximal end and the distal end of the sheath body, and each second member comprising a second material having a second elastic modulus that is higher than the first elastic modulus; and a plurality of third members, each third member being at least partially encapsulated within a given second member of the plurality of second members and extending parallel to the longitudinal axis between the proximal end and the distal end of the sheath body, and each third member comprising a third material having a third elastic modulus that is higher than the second elastic modulus, wherein the sheath body is configured to be radially expandable from an unexpanded state to an expanded state to allow passage of a portion of a medical device through the lumen, the portion of the medical device having a transverse cross-sectional area larger than a transverse cross-sectional area of the lumen when the sheath is in the unexpanded state.
 2. The expandable sheath of claim 1, wherein the second material comprises at least one of: polyether ether ketone (PEEK), a polyether block amide, a polyethylene material, a high-density polyethylene (HDPE) material, a medium-density polyethylene (HDPE) material, a low-density polyethylene (LDPE) material, or a material with an elastic modulus of about 40 ksi.
 3. The expandable sheath of claim 1, wherein the first material comprises at least one of: ethylene-vinyl acetate (EVA), styrene-butadiene copolymer (SBC), synthetic rubber, an elastomer, a material with an elastic modulus of about 1.6 ksi, or a material with a yield strain in excess of 200%.
 4. The expandable sheath of claim 1, wherein the sheath body is configured to automatically return to the unexpanded state after passage of the portion of the medical device.
 5. The expandable sheath of claim 1, wherein a diameter of the outer surface at the proximal end of the sheath body is larger than a diameter of the outer surface at the distal end of the sheath body, when the sheath is in the unexpanded state.
 6. The expandable sheath of claim 1, wherein the third material comprises at least one of: steel, stainless steel, or nitinol.
 7. The expandable sheath of claim 1, further comprising a hub coupled to the proximal end of the sheath body, the hub having at least one hemostatic valve in communication with the lumen of the sheath body.
 8. The expandable sheath of claim 1, wherein at least a portion of the inner surface has an irregular geometry comprising at least one of: ribs, projections, or indentations.
 9. The expandable sheath of claim 1, wherein the inner surface comprises at least one rib extending between proximal and distal ends of the sheath body.
 10. The expandable sheath of claim 1, further comprising a tapered tip attached to the distal end of the sheath body, the tapered tip comprising an outer surface that is continuous with the outer surface of the sheath body, and which reduces in diameter as it approaches a distal end of the tapered tip.
 11. The expandable sheath of claim 10, wherein the tapered tip further comprises an inner surface that is continuous with the inner surface of the sheath body, and which reduces in diameter as it approaches a distal end of the tapered tip.
 12. The expandable sheath of claim 11, wherein the inner surface of the tapered tip defines a tip lumen that extends between the distal end of the sheath body and the distal end of the tapered tip, the tip lumen being in fluid communication with the lumen of the sheath body.
 13. The expandable sheath of claim 12, wherein the diameter of the inner surface at the distal end of the tapered tip is configured to seal against a second portion of the medical device, the second portion of the medical device having a transverse cross-sectional area smaller than a transverse cross-sectional area of the lumen when the sheath is in the unexpanded state.
 14. The expandable sheath of claim 10, wherein the tapered tip comprises at least one of: ethylene-vinyl acetate (EVA), styrene-butadiene copolymer (SBC), synthetic rubber, an elastomer, a material with an elastic modulus of about 1.6 ksi, or a material with a yield strain in excess of 200%.
 15. The expandable sheath of claim 10, wherein the tip comprises the first material.
 16. The expandable sheath of claim 1, wherein the second elastic modulus is substantially higher than the first elastic modulus.
 17. The expandable sheath of claim 10, wherein the outer surface of the tapered tip terminates in a rounded edge at the distal end of the tapered tip.
 18. The expandable sheath of claim 1, wherein each second member is fully encapsulated within a given cavity of the plurality of cavities of the first member.
 19. The expandable sheath of claim 1, wherein each third member is fully encapsulated within a given second member of the plurality of second members.
 20. The expandable sheath of claim 18, wherein each third member is fully encapsulated within a given second member of the plurality of second members. 